1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display (LCD) device and a method of driving the same.
2. Discussion of the Related Art
Until recently, display devices have typically used cathode-ray tubes (CRTs). Presently, many efforts and studies are being made to develop various types of flat panel displays, such as liquid crystal display (LCD) devices, plasma display panels (PDPs), field emission displays, and electro-luminescence displays (ELDs), as a substitute for CRTs. Of these flat panel displays, LCD devices have many advantages, such as high resolution, light weight, thin profile, compact size, and low voltage power supply requirements.
In general, an LCD device includes two substrates that are spaced apart and face each other with a liquid crystal material interposed between the two substrates. The two substrates include electrodes that face each other such that a voltage applied between the electrodes induces an electric field across the liquid crystal material. Alignment of the liquid crystal molecules in the liquid crystal material changes in accordance with the intensity of the induced electric field into the direction of the induced electric field, thereby changing the light transmissivity of the LCD device. Thus, the LCD device displays images by varying the intensity of the induced electric field.
FIG. 1 is a block diagram of a LCD device according to the related art.
Referring to FIG. 1, the LCD device 10 includes a liquid crystal panel 20 displaying images, a backlight unit 30 supplying light to the liquid crystal panel 20, a driving circuit portion 40 operating the liquid crystal panel 20 and the backlight unit 30.
The liquid crystal panel 20 includes first and second substrates facing each other and a liquid crystal layer between the first and second substrates. The liquid crystal panel 20 includes a plurality of gate lines GL1 to GLn along a first direction and a plurality of data lines DL1 to DLm along a second direction. The plurality of gate lines GL1 to GLn and the plurality of data lines DL1 to DLm cross each other to define a plurality of sub-pixel regions. In each sub-pixel region, a thin film transistor T, a liquid crystal capacitor Clc and a storage capacitor Cst are formed.
The backlight unit 30 is below the liquid crystal panel 20 and supplies light to the liquid crystal panel 20 according to control of the driving circuit portion 40.
The driving circuit portion 40 includes a timing controller 50, a gate driving portion 70 and a data driving portion 60. Each of the gate driving portion and the data driving portion includes a plurality of drive ICs.
The timing controller 50 is supplied with signals and image data from an external system and generates control signals to control the gate driving portion 70, the data driving portion 60, and the backlight unit 30. The control signals and the image data are supplied to the corresponding component of the gate driving portion 70, the data driving portion 60, and the backlight unit 30.
The gate driving portion 70 performs ON/OFF operations of the thin film transistors T in response to the control signals from the timing controller 50. The gate lines GL1 to GLn are sequentially scanned by one row line each for one horizontal period. For the horizontal period, the corresponding thin film transistors T are turned on, and data voltages for the corresponding row line pass through the thin film transistors T and applied to the liquid crystal capacitors Clc and the storage capacitors Cst.
The data driving portion 60 selects a reference voltage corresponding to the image data. The selected reference voltage is applied as the data voltage to the liquid crystal panel 20.
Recently, driving methods to reduce a power consumption of the backlight unit 30 have been proposed. The driving methods minimize a luminance of a backlight unit 30 for a low gray level, and more particularly, a luminance for a black. Accordingly, a power consumption of the backlight unit 30 is reduced, and a contrast ratio of the LCD device is improved. Further, by using the driving methods, a dynamic contrast ratio is improved. In other words, when images are displayed for a plurality of frames, brightnesses corresponding to minimum gray levels of the images are reduced, and thus the dynamic contrast ratio is improved.
Of these driving methods, there is a driving method that performs a gray level conversion for an image data of a low gray level and reduces a luminance of a backlight unit, thus displays an image having substantially the same brightness as an image displayed by a normal mode. In this driving method, a correlation analysis between a brightness of an input image data and a luminance of a backlight unit is performed, and according to the correlation analysis, the image data is converted and supplied to a liquid crystal panel and the luminance of the backlight unit is reduced.
However, in case of displaying an image including a plurality of image data of high gray levels, when an image data conversion is performed, image data of more than a predetermined gray level are all saturated and have in common a maximum gray level. Accordingly, display quality may be degraded.
To prevent this problem, for a particular image including image data, a number of which is equal to or more than a reference number and which each have a gray level equal to or more than a reference gray level, an image data conversion and a luminance reduction of a backlight unit are not performed, and a normal mode which does not make the image data conversion and the luminance reduction is performed. For other type of image, the image data conversion and the reduction of luminance are performed. However, since the particular image is not operated in a power consumption reduction mode, reduction of power consumption is limited.